Diesel fuel injection equipment, such as common rail system, equip all modern diesel engines. In these systems, an electric pump sucks the fuel from the fuel tank and sends it to a high pressure pump then, to the common rail that feeds all injectors. The high pressure pump is typically driven by the engine crankshaft and its inlet and outlet are controlled by valves. When the engine is requested to accelerate, in a so-called “foot-on” mode, the pressure inside the common rail is at its highest level and, to the opposite, when the engine decelerates, in “foot-off” mode the fuel is injected at a much lower pressure. Consequently the pressure in the rail raises and decreases quickly and often. The decrease of the pressure is normally done by opening a high pressure valve letting the fuel at high pressure return to the fuel tank. The energy spent to pressurise this fuel is then lost.